Writing on the optical recording medium or reading out from such a medium is carried out by converting a laser beam by a collimate lens to a parallel light, which is then focused by an object lens. Such collimate lens and object lens are produced usually by heating a preform made of glass or a resin to its softening point, followed by precision pressing.
In recent years it has been proposed to utilize a violet laser beam having a wavelength of from 400 to 415 nm (typical wavelength being 405 nm) in order to increase the recording density of an optical recording medium, and an optical glass or lens suitable for such a proposal is disclosed (see Patent Document 1).
Patent Document 1: JP-A-2004-43294